Adamantium is the fictional metal bonded to Wolverine’s skeleton in the X-Men films.
The procedure is shown most directly in X-Men Origins: Wolverine, where the Weapon X program coats Logan’s bones and claws with the nearly indestructible alloy. The process is extremely painful, and Logan survives partly because his mutant healing ability repairs the damage caused by the operation.
Adamantium gives Wolverine’s claws their distinctive strength and makes his skeleton highly resistant to injury. It is also associated with the metallic sound and visual design that identify the character in the films.
Adamantium is a Marvel fictional material and should not be confused with vibranium, another Marvel metal most strongly associated with Black Panther and Captain America. Carbonadium is also a different fictional alloy appearing elsewhere in Marvel stories.